The present invention relates generally to medical devices and particularly to a balloon catheter with dilation elements on the surface of the balloon.
Balloon catheters are widely used in the medical profession for various intraluminal procedures. One common procedure involving the use of a balloon catheter relates to angioplasty dilation of coronary or other arteries suffering from stenosis (i.e., a narrowing of the arterial lumen that restricts blood flow).
Although balloon catheters are used in many other procedures as well, vascular angioplasty using a balloon catheter has drawn particular attention from the medical community because of the growing number of people suffering from vascular problems associated with arterial stenosis. This has lead to an increased demand for medical procedures to treat such problems. The widespread frequency of vascular problems may be due to a number of societal changes, including the tendency of people to exercise less while eating greater quantities of unhealthy foods, in conjunction with the fact that people generally now have longer life spans than previous generations. Angioplasty procedures have become a popular alternative for treating arterial stenosis because angioplasty procedures are considerably less invasive than other alternatives. As an example, stenosis of the coronary arteries has traditionally been treated with bypass surgery. In general, bypass surgery involves splitting the chest bone to open the chest cavity and grafting a replacement vessel onto the heart to bypass the blocked, or stenosed, artery. However, coronary bypass surgery is a very invasive procedure that is risky and requires a long recovery time for the patient.
To address the increased need for vascular treatments, the medical community has turned to angioplasty procedures, in combination with stenting and other procedures, to avoid the problems associated with traditional open surgery. Typically, angioplasty procedures are performed using a balloon-tipped catheter that may or may not have a stent mounted on the balloon (also referred to as a stented catheter). The physician performs the angioplasty procedure by introducing the balloon catheter into a peripheral artery (commonly one of the leg or arm arteries) and threading the catheter to the narrowed part of the artery to be treated. During this stage, the balloon is uninflated and collapsed onto the shaft of the catheter in order to present a low profile which may be passed through the vasculature. Once the balloon is positioned at the narrowed part of the artery, the balloon is expanded by pumping a mixture of saline and contrast solution through the catheter to the balloon. As a result, the balloon presses against the inner wall of the artery to dilate it. If a stent is mounted on the balloon, the balloon inflation also serves to expand the stent and implant it within the artery. After the artery is dilated, the balloon is deflated so that it once again collapses onto the shaft of the catheter. The balloon-tipped catheter is then retracted from the body. If a stent is mounted on the balloon of the catheter, the stent is left permanently implanted in its expanded state at the desired location in the artery to provide a support structure that prevents the artery from collapsing back to its pre-dilated condition. Alternatively, if the balloon catheter is not adapted for delivery of a stent, either a balloon-expandable stent or a self-expandable stent may be implanted in the dilated region in a follow-up procedure. Although the treatment of stenosed arteries is one common example where balloon catheters have been used, this is only one example of how balloon catheters may be used and many other uses are also possible.
One problem that may be encountered with conventional angioplasty techniques is the proper dilation of stenosed regions that are hardened and/or have become calcified. Stenosed regions may become hardened for a variety of reasons, such as the buildup of atherosclerotic plaque or other substances. Hardened regions of stenosis can be difficult to completely dilate using conventional balloons because hardened regions tend to resist the expansion pressures applied by conventional balloon catheters. One solution that has been offered for dilating hardened stenoses is special balloon catheters with dilation wires or beads that extend along the length of the balloon. The dilation wires and/or beads focus that dilation pressure of the balloon onto the narrower contact area between the dilation wire or bead and the vessel wall. As a result, the increased, focused pressure may crack and/or break up the hardened stenosis, thereby allowing the vessel lumen to be expanded.
One approach that has been used to attach dilation wires and/or beads to a balloon is securing the wires and/or beads to the exterior surface of the balloon with adhesives. However, the use of adhesives to secure dilation wires and/or beads has several disadvantages. For example, there may be concern that the adhesive could detach from the balloon surface and allow the dilation wire and/or bead to break loose. This may be a particular concern when the adhesive is the only or the primary mechanism for securing the dilation wire and/or bead to the balloon surface. Detachment of the adhesive from the balloon surface can be a more serious problem when the balloon is made of a compliant or semi-compliant material, because the balloon material stretches as the balloon expands but the dilation wire and/or bead may not stretch during expansion or may stretch at a different rate. Because of these opposing forces between the balloon material and the dilation wire and/or bead, the adhesive may crack or lose its adherence to the balloon surface. Moreover, even in the case of non-compliant balloons, detachment of the adhesive may be a concern because physicians are particularly adverse to any possible risk of intravascular device failures. The use of adhesives in a manufacturing setting is also disadvantageous. Applying adhesives during the manufacturing process is typically a manually intensive task and time consuming. Maintaining cleanliness standards is also more difficult with the presence of adhesives, since adhesives are generally messy. The use of adhesives also requires extra fixturing to temporarily secure the parts being adhered while the adhesive cures.
One solution to the problem of attaching separate dilation wires and/or beads to the surface of a balloon is to make the dilation element an integral structure with the balloon wall. However, a disadvantage with this approach is that typical materials used to make angioplasty balloons are required to have a certain amount of flexibility and/or elasticity in order to enable formation of the balloon in manufacturing and to perform in the desired fashion in medical procedures. For example, thermoplastic materials are often used to make angioplasty balloons due to their formability properties and their suitability in medical procedures. However, unlike separate dilation elements that can be made from a hard metal and adhered to the balloon surface, integral dilation elements are limited by the material properties of the balloon material. Although an integral dilation element may be co-extruded using a different material that is harder than the material used for the balloon wall, such co-extruded dilation elements are still limited to using materials that are compatible with the material of the balloon wall. Moreover, where the material of the dilation element is the same as the material of the balloon wall, the properties of the dilation element are further limited. Thus, integral dilation elements are typically less capable of dilating hardened stenoses than a comparable separate dilation element made from hard metal.
Accordingly, the inventors believe it would be desirable to provide a balloon catheter with an improved integral dilation element.